5. High clouds are composed primarily of ice crystals, whereas low clouds are composed primarily of water
droplets. This difference is most likely because the
average air temperature at altitudes from:
A. 0 km to 3.2 km is at or below Or whereas the
average air temperature at altitudes Trom 3.2 km to
6.0 km is above 0°C.
B. O km to 3.2 km is at or below 0°C, whereas the
average air temperature at altitudes from 6.0 km to
16.0 km is above 0°C.
C. O km to 3.2 km is above 0°C, whereas the average
air temperature at altitudes from 3.2 km to 6.0 km
is at or below 0°C.
D. O km to 3.2 km is above 0°C, whereas the average
air temperature at altitudes from 6.0 km to 16.0 km
is at or below 0°C.

Choose the incorrect statement (a) the motor end plate membrane is only capable of generating graded potentials, but it is contiguous with the skeletal muscle sarcolemma, which can generate action potentials. (b) propagation of an action potential through the t-tubules into the sarcoplasmic reticulum triggers the release of ca++ into the cytoplasm of a skeletal muscle fiber. (c) the generation of suprathreshold endplate potentials in multiple muscle fibers could be due to the increased frequency of action potential generation at the axon hillock of a single motor neuron. (d) a greater amount of ach would be found in the presynaptic vesicles of a motor unit that fired several action potentials after exposure to botulinum toxin, than in a motor unit that fired several action potentials after exposure to the venom of the krait snake (which contains α-bungarotoxin).